John Gill Commentary Isaiah 8:3

"And I went unto the prophetess; and she conceived, and bare a son. Then said Jehovah unto me, Call his name Maher-shalal-hash-baz." — Isaiah 8:3 (ASV)

And I went unto the prophetess His wife, so called; not because she prophesied, but because she was the wife of a prophet; and besides, the birth of her son later mentioned, and his name, had in them the nature of a prophecy. The phrase of going unto her is an euphemism, a modest way of expressing the conjugal debt:

and she conceived and bore a son; which Jarchi would have the same with Immanuel in (Isaiah 7:14) but this is a later prophecy, and a distinct one from that; and not only the names of the children are different, but the mothers also; the one a virgin, the other the prophet's wife.

Then said the Lord to me, call his name Mahershalalhashbaz: of the signification of this name, (See Gill on Isaiah 8:1). Kimchi thinks that his name did not consist of these four words, only of two of them; and that he was sometimes called "Mahershalal", and sometimes "Hashbaz": both signifying the same thing.

Some think that all this was done only in a vision, and not in reality, to declare and confirm what follows; though by that it seems rather to be a real fact.